Communication with moving vehicles



Nov. 7, 1933. EsPENscHlED Er AL 1,933,795

- COMMUNICATION WITH MOVING VEHICLES Original Filed Sept. 10. 1951.Filter Slynal Circuit with Sq-oerz'mosed Couv-lle( Lep/wl/Le Cirzcuit@camel-awf- 2126er 12e/77nd.

C ATTORNEY Patented Nov. 7, 1933 UNITED STATES COMMUNICATION WITH MOVINGVEHICLES Lloyd Espenschied, Kew Gardens, and Newton Monk, New York, N.Y., assignors to American` Telephone and Telegraph Company, acorporation of New York Application September 10, 1931, Serial No.562,179 Renewedv March 24,. 1933V 4 Claims.

This invention relates to telephone communication with moving vehiclesand more especially with trains. Its object is to provide a system inwhich the coupling between a train circuit and a fixed circuit shallremain substantially constant and free from" such irregularities asoccur when the coupling is directly with a transmission line on polesalong the route, such irregularities arising largely because of varyingdistance between the pole line and the track. A further object is toprovide a system in which the space to be bridged between the traincircuit and the fixed circuit is less than when coupled directly to thetransmission line. Still a further object is to reduce the amount ofpower supplied to the signaling channels by reducing the attenuation inthe various portions of the signal channel.

Broadly, these objects are attained by using the conductors of the poleline for bringing the voice frequency signals to any one of a number ofquite widely spaced stations along the route at which the message isshifted to a carrier frequency and superposed on the same or adjacenttransmission circuits on the pole line. Circuit taps are led from thistransmission line to the track, one at each block junction in a blocksignaling system and the rails of a block are used in series as part ofthe path of the high frequency circuit. On the trains, in the rear ofthe end car, are located coupling coils so mounted as to be in inductiverelation wih the rails. There may be one set of these coupling coils forboth transmitting and receiving or there may be separate sets of coilsone for transmitting and one for receiving. These coils are connected tothe necessary modulators, demodulators and amplifiers and thenceto atelephone set, all of which are located on the train. In order to reduceattenuation losses, only those blocks occupied by trains have thecircuits to the rails completed and the control of this feature residesin and is operated by the block signaling system.

The invention will be better understood by reference to the followingspecication and accompanying drawing in which Figure 1 shows a preferredform of circuit for the stationary portion of our signaling system; Fig.2 shows the circuit of the train with which communication is to bemaintained and Fig. 3 is a modiiication of Fig. 1 wherein AC currentsinstead of DC currents are used in the block signaling system.

Referring more particularly to Fig. 1, there is shown a portion of trackcomprising three blocks and paralleling this track is shown atransmission line L with a iixed station 10 to which the voice frequencysignals may be brought over the voice frequency circuit L parallelingthe track or from some other remote point. Such fixed stations would beprovided at intervals along the route of some fty or one hundred milesseparation, the route thus constituting a plurality of sections. Whileit is not necessary to do so, we find it desirable, in order to obtainbetter inductive coupling with the train, to shift the voice frequencymessage to a carrier frequency at the station 10. The vresulting carrierfrequency signal is then superposed on the transmission line L whichcarries the voice frequency message or on other transmission linescarried by the same pole line. In order to confine the `modulatedcarrier wave to the section of the line involved, suitable blockingdevices such as low-pass filters .11 would be introduced as needed ateach fixed station 10.

A plurality of tapping circuits 15 come from the line L; one for eachblock of the railroad, it being understood that such blocks would, ingeneral be of a length of about a mile. i In order to minimizeattenuation losses, however, we provide means whereby only those blocksoccupied by a train shall have the connection completed from the line Lto the tracks and the provision whereby this is attained will now bedescribed.

The figure shows a typical block signaling circuit supplied with directcurrent, one of these circuits being shown for each of the three blocksof the figure. The elements necessary for this circuit and theirfunction will behest understood by describing the operation of thesystem. If, for instance, the train enters block C in which the circuitcondition was that shown in block A, then` current from a battery andpole changer 17 at the remote end of block C is short-circuited throughthe axles of the train and a relay Rc which was formerly activated isnow released and circuit from battery 19e` is broken, whereupon thesignal 20c is set to stop position. The relay Rc is a polarized relaywith a double armature 21 and a polarized armature 22, the latterchanging only on reversal of current. The moving of the signal 20cshifts the pole changer 17h in the block B mechanically to the left-handposition shown in the figure, this being accomplished by any suitablemechanism indicated by 18. Before the train left the block B, the signal2Gb had also been in stop position but upon the shifting of the polechanger 17h current is reversed through the relay Rb so operating thetwo armatures as to shift the signal to the caution position. Suchmotion of this signal, however, brings the pole changer 17a into itsnormal position, whereupon system of block signaling is well known inthe art and does not, in itself, constitute a part of our invention. Ineach of these circuits, however,

and in series with each R relay, is introduced an additional relay Swhich, when the relay S is excited, breaks the circuit connection 15from the line L to the rails of the given block. Since the R and Srelays are excited for all blocks except those occupied by a train, itwill be seen that the only blocks to which circuit is completed fromline L to the track are those in which a train is present and whencircuit is so completed as in block C, the carrier signal is brought tothe block at the junction point and high frequency current may Viiowthrough these rails and through an axle of the train. Condensers C1 arepreferably introduced in the lines 15 to keep out the direct currentsupply of the relays R and S. As the train now proceeds from block toblock in the direction indicated by the arrow, each succeeding circuitcomes into action as indicated and finally returns to its normalposition two blocks in the rear of the train. It is obvious that thefunctiony of the S relays could be performed by the R relays throughadditional -armatures thereon.

Fig.- 2 shows the cooperating circuit on the moving train. In thisfigure, there are shown two sets of coils carried by the train at therear and preferably as close to the track circuit as is feasible. Theoneset of coils 23 picks up the' high frequency signal from the trackand passes it through a lter and demodulator amplifier to a telephoneset 24. For signaling in the reverse direction, voice frequency from theset 24 passes to an oscillator-modulator-ampliiier equipment of the sameor a different carrier frequency through a lter to the set of coils2'7-'from whence the signal is transferred to the rails and accompanyingcircuit to the subscriber connected t0 station 10. In this gure we haveshown the usual type of hybrid coil connection 29 for twoway signaling,this being old in the art.

From the description of the invention as thus given, it is seen that atwo-way telephone channel may be established between the train and aremote subscriber under circumstances which ykeep to a minimumattenuation losses and the sudden and large changes in transmissionlevel characteristic of previous systems for communication with movingtrains. additions can be made to the invention as thus far described.For example, it will be recognized thatas the train recedes from thejunction point, there will be a drop in transmission llevel due toattenuation losses resulting from imperfect insulation of the track.-Since, however, the block sections are comparatively short, such losswill not be excessive and furthermore may be-substantially reduced byautomatic means for changing the gain of the amplifiers in such a manneras described in connection with the application of Aflel and Green,Serial No. 396,893, led October 2, 1929. Also, to reduce the shunt lossdue to the conductors 15 attached to the telephone line at each block,we may locate the S relays on the telephone pole lines.

It is evident that with the train running in the direction indicated, itwill be necessary to carry the coils 23 and 27 to the rear of the lastaxle of the train. These coils may, on the other hand, be placed in thefront of the train but in that event, it will be necessary also to makethe connection of the block signaling circuit at the vother end of theblock which will require certain Various changes or rearrangements ofoperation in order that the system shall function in the proper order.It will also be noted that whenever the rear axle of the last car on thetrain is in one block and the coupling coils are coupled to the rails ofthe next block in the rear, no energy will be received by the coils. Thetime interval for this condition will usually be extremely-short but, ifso desired, we may overcome this defect by making the S relays of theslow-release type or, as an alternative, the connections may be arrangedso that carrier frequency energy is fed simultaneously to the blockcontaining the train and the block to the rear, or additional blocks ifadvisable.

Fig. 3 shows a modification of Fig. 1 in which the block signalingsystem is operated by alternating current instead of direct current. Inthis case the batteries associated with the pole changers 17 arereplaced by transformers'Sl and 31a and the R and S relays are ACoperated relays.

In this gure, as a further modication, we have also shown the modulatedcarrier frequency signal as superposed on the signal circuit L1 whichprovides AC power from a generator 34 for the block signaling system.The signal arrangement shown in this figure is a common form ofthreeposition alternating current control signaling circuit, the Rrelays comprising a permanently connected AC winding 32 and the winding33 in which the phase of the current is controlled by the position ofthe pole changer associated with the same block. The S relays, added inseries with the R relays, operate simultaneously with them to connectthe carrier telephone circuit to the track in the particular block inwhich the train is located. 'A high pass filter or its equivalent isincluded in each telephone tap circuit to exclude the block signalfrequency. With these exceptions, the operation of the system as a wholeis the same as that described in connection with Figs. 1 and 2 and willbe readily understood from that description.

In the case of more than one train operating on the same track,comunication may be effected by a party-line arrangement or by the useofdifferent carrier frequency channels, separation being obtained by lterslocated at the terminal point on the trains. Where a number of trainsare running on several different tracks, it might be preferableto usedifferent pairs of the line wires carried on pole lines and to employdifferent carrier frequency channels, as will be apparent to thoseskilled in the art.

While 'the invention has been described as showing the rails of a givenblock connected in series through an axle of the train for the carrierfrequency as well as the block signaling circuit,`

it is evident that the carrier frequencies may be connected to a railcircuit comprising the two rails in parallel with a ground or a separatewire return. Such a circuit may be employed for communication in one orin both directions and has the advantage that it permits the placing ofthe coupling coils at any point along the train instead of to the rearof the last axle.

A fixed station may serve the section of transmission between itself andthe next fixed station in one direction or may serve a. section of thesame length with the station at the middle. In the latter case the lowpass filters 11, or their equivalent, would be placed midwayt betweenstations.

What is claimed is:

1. In a system for communicating with moving trains and cooperatingwitha block signaling system, a transmission line along the train route, asource of voice frequency signals, fixed stations along said route,means for shifting incoming voice frequency signals to a carrierfrequency and superposing the carrier frequency message on thetransmission line, means for impressing the carrier frequency signals onthe blocks occupied by a train, and a device on the train for picking upthe carrier frequency signal in its block.

2. In a system for communicating with moving trains and cooperating witha block signaling system, a Vtransmission line along the train route forvoice frequency signals, fixed stations along said route for shiftingthe voice frequency signal to a carrier frequency and superposing thecarrier frequency message on the transmission line, connections from thetransmission line to the rails of each block, a device on the trains forpicking up the high frequency signal, and means for activating onlythose blocks occupied by a train.

3. In a system for communicating with moving trains and cooperating witha block signaling system, a transmission line along the train route forvoice frequency signals, xed stations along said route for shifting thevoice frequency signal to a carrier frequency andsuperposing the carrierfrequency message onv the transmission line, connections from thetransmission line to the rails of each block, a device on the trains forpicking up the high frequency signal, and means controlled by the blocksignaling system for activating only those blocks occupied by a train.

4. In a system for communication with moving trains, and cooperatingwith a block signaling system, a transmission line along the train routefor voice frequency signals, fixed stations along the route separated bya distance large compared to the length of a block, means at thestations for receiving a subscribers message and for shifting .it toV acarrier frequency and superposing the carrier frequency message on thetransmission line, means for confining the modulated carrier frequencyWave from any one fixed station to a section of transmission lineadjacent that xed station, a plurality of taps on this section one foreach block adapted to connect the transmission line to any block in thatsection, and means controlled by the block signaling system foractivating only those blocks adjacent to the train.

LLOYD ESPENSCHIED. NEWTON MONK.

